Genetic sequence of brown-rot fungus reveals enzymes

By Ryan C. Christiansen

Postia placenta, more commonly known as brown-rot fungus, an organism that efficiently colonizes and decays wood, is unique in the way it breaks down woody biomass, according to the U.S. DOE Joint Genome Institute. The fungus can rapidly depolymerize the cellulose in wood without removing the lignin.

Now, researchers at the Joint Genome Institute in Walnut Creek, Calif., and the USDA Forest Service Forest Products Laboratory in Madison, Wis., have translated the genetic code of the fungus so that its biomass-degrading enzymes might be leveraged to pretreat biomass for the production of biofuels, such as ethanol.

According to the institute, the findings explain the biochemistry that makes the thread-like fungi uniquely destructive to wood. The genetic sequence provides researchers with a detailed inventory of its biomass-degrading enzymes.

"P. placenta has, over its evolution, shed the conventional enzymatic machinery for attacking plant material," said Dan Cullen, a scientist at the Forest Products Laboratory. "Instead, the evidence suggests that it utilizes an arsenal of small oxidizing agents that blast through plant cell walls to depolymerize the cellulose. This biological process opens a door to more effective, less-energy intensive and more environmentally sound strategies for more lignocellulose deconstruction."

The DOE and USDA laboratories previously sequenced the genome of white-rot fungi, which simultaneously degrades lignin and cellulose. "For the first time, we have been able to compare the genetic blueprints of brown-rot, white-rot and soft-rot fungi, which play a major role in the carbon cycle of our planet," said Randy Berka, director of integrative biology at Novozymes Inc. in Davis, Calif., a participant in the study. "Such comparisons will increase our understanding of the diverse mechanisms and chemistries involved in lignocellulose degradation."

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